The present invention relates to a multi-cylinder internal combustion engines, and specifically to such an engine incorporating engine exhaust recirculation (EGR) wherein certain of the cylinders is selectively disable when reduced power output can operate the vehicle without adversely affecting the performance of EGR.
Variable cylinder disablement is known in the art to improve fuel economy by selectively shutting off fuel supply to several cylinders of the engine when reduced power output can operate the vehicle adequately. This disablement, known as variable displacement control, is particularly advantageous for application to electronic fuel injection because the fuel injectors can be electrically disabled to cut off fuel without having the need for mechanical parts to shut off intake valves which would otherwise be required in carbureted engines. On the other hand, exhaust gas recirculation is also known as an effective means for minimizing the harmful product NOx by recirculating a portion of exhaust emissions through combustion chambers. However, when EGR is used in conjunction with the variable displacement internal combustion engine where several cylinders are unfueled, and the unfueled cylinders draw in air and exhaust it through exhaust manifold. This is likely to result in a greater oxygen content than is intended for normal EGR operations. Therefore, exhaust gas recirculation cannot properly operate.